1. Field of Invention
The present invention relates to a valve lift apparatus. More particularly, the present invention relates to a variable valve lift apparatus that varies a lift amount of a valve opening/closing an intake port or an exhaust port of an internal combustion engine in multi steps.
2. Description of Related Art
An internal combustion engine generates power by burning fuel in a combustion chamber in an air media that is drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open.
In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on a rotation speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotation speed of the engine.
For example, research has been undertaken for a variable valve lift (VVL) apparatus that enables different lifts depending on engine speed, and for a variable valve timing (VVT) apparatus that opens/closes the valves with different timing depending on the engine speed.
Meanwhile, in a structure that a rocker arm is disposed on a rocker arm shaft and a cam pushes one side of the rocker arm to move a valve that is disposed at the other side of the rocker arm, researches have been undertaken so as to control the movement of the valve in multi steps.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.